1. Field of the Invention
The present invention relates to a fuel supply system for a vehicle and, more specifically, to a fuel supply system for a vehicle which can reduce fuel consumption of a vehicle engine.
2. Description of the Related Art
FIG. 7 to FIG. 9 show a fuel supply system for a vehicle disclosed in United States Patent application preceding to the application of the invention (U.S. Ser. No. 10/391,614, filing date: Mar. 20, 2003, hereinafter simply referred to as “precedent application”.).
In FIG. 7, a fuel pump 1 includes a pump body 1a, an electric motor unit 1b for driving the pump body 1a, and a check valve 1c for enhancing startability of the engine by filling a fuel system including a fuel piping 3 when an engine 5 is stopped, described later, with fuel, and is disposed in a fuel tank 2. The fuel pump 1 is connected to a fuel pressure regulator 7 for controlling the fuel pressure in the fuel piping to a predetermined controlled pressure via the fuel piping 3, a pressure accumulator 30 for accumulating the pressure of the fuel pumped into the fuel piping 3, a pressure detector 22 for measuring the fuel pressure in the fuel piping 3, and a fuel injection valve 4.
The fuel injection valve 4 is connected to an intake pipe 6 of the engine 5, and is adapted to be controlled by the engine control unit 20 and to supply fuel to the engine 5.
A switch relay 21 is controlled to stop power distribution to the motor unit 1b of the fuel pump 1 from a power source E by opening a contact point 21a when the pressure in the fuel piping 3 reaches a first set pressure P1 by a pump control unit 20a of the engine control unit 20, and start power distribution to the motor unit 1b by turning the contact point 21a on when the pressure in the fuel pump 3 is reduced to a second set pressure P2 which is lower than the first set pressure P1.
The fuel pressure regulator 7 includes a spring chamber 8 and a pressure regulating chamber 9 divided by a diaphragm 10. A spring 8a is disposed in the spring chamber 8 so that the spring 8a presses the diaphragm 10 at a predetermined control pressure toward the pressure regulating chamber 9.
The pressure regulating chamber 9 includes a discharge port 9a and a valve member 9b mounted to the diaphragm 10 for opening and closing the discharge port 9a. The spring chamber 8 is brought into communication with the upstream side of the fuel injection valve 4 in the intake pipe 6 via a branch piping 11a, and the pressure regulating chamber 9 is brought into communication with the fuel piping 3 via a branch piping 11b. In addition, the pressure regulating chamber 9 is brought into communication with the fuel tank 2 via the discharge port 9a and a return piping 12.
The engine control unit 20 includes the pump control unit 20a and a fuel calculation control unit 20b, and the fuel calculation control unit 20b calculates the required amount of fuel supply based on the air quantity sucked by the engine 5, with the premise that the pressure difference between the front and the back of the fuel injection valve 4 is kept constant, and the valve opening time of the fuel injection valve 4 is controlled. In this case, as a method of calculating the required amount of fuel supply to the engine 5 by the fuel calculation control unit 20b, so-called a D-jetronic system, which calculates the required amount of fuel supply based on the pressure in the intake pipe 6 measured directly by an intake pipe pressure detector 14, is employed. However, it is also possible to employ a L-jetronic system in which an airflow sensor is mounted to the intake pipe 6 to calculate the required fuel amount based on the intake air amount per unit time of the engine 5 detected by the airflow sensor instead of the intake pipe pressure detector 14.
The pressure accumulator 30 is disposed so as to communicate with the fuel piping 3 as shown in an enlarged view in FIG. 8 and a detailed view of a diaphragm in FIG. 9, and includes a storage chamber 32 adapted to be filled with fuel flown from the fuel piping 3 and expand or contract in the direction of center axis depending on the fuel pressure to vary the capacity.
The storage chamber 32 includes a cylindrical diaphragm 33 formed of nitrile butadiene rubber (NBR) into an accordion shape, a metallic ring 34 of stainless steel embedded in the diaphragm 33 at a predetermined position, and an end plate 35 of a disk shape mounted hermetically at the other end (lower end in FIG. 8, FIG. 9) of the diaphragm 33, and an end (upper end in FIG. 8, FIG. 9) of the diaphragm 33 is hermetically mounted to an inner wall of an enclosure 31 so that the metallic ring 34 is integrally molded when molding the diaphragm.
The storage chamber 32 is adapted to contract in the process of lowering of the fuel pressure in the fuel piping 3 from a third set pressure P3, which is at least lower than the first set pressure P1 and a predetermined control pressure of the fuel pressure regulator, and higher than the second set pressure P2 to the second set pressure P2 to hold a pressurizing force for delivering the fuel in the storage chamber 32 to the fuel piping 3. The pressure accumulator 30 is disposed in an engine room, in a fuel pressure regulator, or in the fuel tank, although it is not shown.
Since the fuel supply system for a vehicle in the precedent application is configured as shown above, and hence the pressure accumulator 30, which communicates with the fuel piping 3 and is filled with fuel flown from the fuel piping, is disposed in the engine room, in the fuel pressure regulator, or in the fuel tank, there was a problem in that it was necessary to secure a space for disposing the pressure accumulator 30 therein and hence the manufacturing cost increases.
Also, since the pressure accumulator 30 has a complex structure as described above, when disposing the pressure accumulator 30 in the engine room, in the fuel pressure regulator, or in the fuel tank, there was a problem in that a significant cost was required for devising a countermeasure for deterioration of a movable portion due to vertical vibrations during normal travel or a countermeasure for enhancement of the durability for the case of collision.
In addition, in the fuel pump control means in the precedent application, since the fuel pump 1 is driven by an ON/OFF signal, fuel is discharged at a maximum capacity from the fuel pump 1 while ON signal is emitted. Therefore, there was a problem in that after the fuel pressure reaches the first set pressure P1 and then the pump is stopped, fuel continues to flow back to the fuel tank 2 uselessly for a while due to inertia of the motor unit 1b of the fuel pump 1.
Also, in the fuel pressure correcting means of the precedent application, the valve opening period of the fuel injection valve 4 is controlled so that the amount of fuel supply calculated based on the output of the fuel pressure detector can be obtained for each calculation cycle of the fuel calculation control unit of the engine control unit. Therefore, there was a problem in that when the fuel pressure in the fuel piping 3 varies for a shorter time than the calculation cycle, time lag may occur for the control of the valve opening period of the fuel injection valve 4.
Furthermore, in the fuel pressure regulator 7 in the precedent application, since the fuel discharge port 9a on the upstream of the return piping 12 is constantly opened, there was also a problem in that when the fuel pressure exceeds the control pressure of the fuel pressure regulator at the time when the fuel pump 1 is driven, an useless fuel flowback occurs.